Field of the Invention
The present invention relates to a method for giving robustness to detection of a leak deviating from a tolerable amount when a certain amount of leak from a duct is tolerated, a pipe structure capable of achieving the method, and an aircraft including the pipe structure.
Description of the Related Art
An airframe of an aircraft is provided with a pipe through which high-temperature bleed air from an engine flows (for example, Japanese Patent Laid-Open No. 2014-094663).
As shown in FIG. 12A, a bleed air pipe 80 includes a plurality of ducts 81 and a coupling 82 that connects the ducts 81 together. The coupling 82 clamps flanges (not shown) of the ducts 81 that are abutted against each other.
In the typical bleed air pipe 80 of the aircraft, a sealing material such as a gasket is not provided between the flanges or between the coupling 82 and the flanges in view of a weight reduction and maintainability. A leak of a small amount of bleed air from between the flanges to the outside is tolerated.
While a small amount of leak is tolerated, it is necessary to detect a leak when the coupling 82 is loosened or damaged, and a leak amount from a connection portion of the ducts 81 is increased. Of course, it is also necessary to detect a leak when cracks, corrosion, or the like are generated in the duct 81, and a leak from a body portion of the duct 81 occurs.
When a certain amount of leak is tolerated depending on a portion of the pipe, it is desirable to detect only a leak deviating from the tolerable amount due to damage or the like in the coupling and the ducts without detecting a leak with the tolerable amount.
In order to detect a leak of the high-temperature bleed air from the pipe, a plurality of vent holes 84 are formed in a cover 83 that covers the ducts 81 and the coupling 82 as shown in FIG. 12A. A line-shaped sensor 85, a temperature of which is increased by the bleed air flowing out from the vent holes 84, is provided. The leak can be detected based on electrical resistance of the sensor 85 that is changed when the temperature is increased.
Here, a temperature of each portion 85A of the sensor 85 that is increased by the bleed air flowing out from the vent hole 84 largely varies due to various factors such as a distance from the vent hole 84 to the portion 85A, movement of a surrounding gaseous body, and fluctuations in temperature/pressure of the gaseous body.
The temperature variation in each portion 85A of the sensor 85 with respect to a flow rate of the bleed air flowing out from the vent hole 84 (referred to as a leak flow rate below) is large in some cases. In this case, it is very difficult to determine an appropriate set temperature at the time of setting a temperature corresponding to a suitable leak flow rate in the leak sensor, and detecting the leak when a temperature equal to or more than the set temperature is sensed by the sensor 85. Depending on the set temperature, a tolerable small amount of leak may be frequently detected, or a surrounding environment of the pipe may have a high temperature due to no detection of a leak deviating from a tolerable leak amount.
In order to avoid the above problems, it is important to provide robustness for the leak detection.
Accordingly, an object of the present invention is to provide a method for giving robustness to leak detection, a pipe structure capable of achieving the method, and an aircraft including the pipe structure.